In agriculture, it is important to be able to sow seed in accurate amounts at a set distance apart. In small scale agriculture this is important in terms of the ready management of a sown field. In large scale agriculture, this is even more important as a small deviation from a desired sowing rate can cause inter-plant competition and reduce yields and increase seed wastage.
A number of metering devices for seed drills are known to ensure accurate and consistent sowing. However, these devices have a number of problems associated with them.
One type of device uses fluted rollers which pick up seed from a seed hopper and distributes the seed to multiple outlets. These fluted rollers however give inconsistent seeding rates as a consequence of the seed being delivered by the cavities of the rollers. In some cases seed may be damaged by the fluted roller.
New Zealand Patent No. 126307 disclosed a revolutionary metering device which had sponge rotor rotating about a horizontal axis and pressed against a funnelled outlet from a seed hopper. The resilient sponge rotor is very effective at picking up individual seeds and metering them to a single outlet on the seed drill.
Unfortunately, this metering device also has problems associated with it.
One problem is that the sponge rotor is difficult to change if it has degraded to a stage where it is no longer efficient. Sponges left on metering devices for a period of time (as a consequence of being difficult to remove) are eaten by vermin, degrade by ultraviolet light or retain permanent impressions as a consequence of seeds left on the rotor. In this particular metering device the rotor is glued to a metal disc which is biased against the funnelled outlet by a complicated arrangement of springs and other biasing means. This arrangement understandably makes it difficult to readily remove the rotor when required in order to maintain the accuracy of the seed drill.
Yet another problem with metering devices is that the seeds being channelled to the rotor can be subject to a phenomenon known as bridging. Bridging is the clumping together of seeds which can block the inlet of the metering device. To overcome this problem agitators are incorporated into the seed drill which adds to the expense and maintenance of the device.
Yet another problem with this metering device is that is gravity affected. For example, in the seeding process the funnel may tilt as the seed drill travels on a slope. This can cause the seed within the funnel to move away from the funnel outlet and thus there may be no seed available for the metering device to distribute.
Yet another problem is that only one outlet per metering unit is possible. Seed drills have multiple outlets (say up to 20) allowing them to sow multiple rows. Thus, with the existing metering devices it is necessary to have a separate metering device for each seed drill outlet. Not only is this expensive, but also bulky. The bulkiness of this system precludes ready use of this metering device with small vehicles such as four wheeled motorbikes.
Many seed drills use either directly or indirectly the rotation of a seed drill wheel to determine the rate at which the seeds are delivered. This is sensible in many situations as if the seed drill is being slowed for a turn, it is desirable that the rate at which the seed is delivered is likewise slowed to keep a consistent distance between the seeds being sowed.
Unfortunately, there is a problem with this system as wheel slippage is common which can cause the metering device to be driven at a rate slower than the seed drill is actually travelling. This leads to greater spacing between the seeds.
Considerable research has been invested into insuring that there is minimal wheel slippage during seed sowing so that the delivery rate of seed is proportional to the rate the seed drill travels over ground. Such research has included provision of spikes or special tyres on the wheels of the seed drill. This is an unfortunate expense and these features do not fully solve the problem.
It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.
Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.